fix: allow user to change password without privileges on _pico_property

Summary

• fix: allow user to change password without privileges on _pico_property

close: #449 (closed)

Ensure that

• New code is covered by tests
• API is documented
• Changelog is up to date
• (if Lua API changed) Lua API version is bumped in luamod.rs
• (if necessary) A follow-up doc issue is created in picodata/docs and linked here